In recent years, fluorescent materials for light-emitting devices used for flat panel displays, high-intensity and low-power consumption lighting, etc. have gained much attention. In regard to such fluorescent materials, development of fluorescent materials or light-emitting materials with less environmental load and free from rare raw materials other than fluorescent lamps using mercury or fluorescent materials containing much rare earths has been required in view of global environmental problems. Furthermore, since high color rendering properties are needed for illumination light sources, the illumination light sources have also been required to have a broad spectrum within a desired wavelength region (color gamut) in a visible light range of about 400 nm to 800 nm in wavelength. In this kind of environment, white light-emitting diodes (LED) or light-emitting devices equipped with them have been attracting attention as new illumination light sources in place of fluorescent lamps or incandescent lamps. Illumination using a light source of white light-emitting diodes closer to practical use provides advantages of high luminance efficiency and longer operating life; therefore, such illumination light sources are expected to be promising in the future.
There are the following configurations in the white light-emitting diodes: (a) purple to blue light-emitting diodes plus yellow light-emitting phosphor fine particles, (b) ultraviolet light-emitting diodes plus various phosphor fine particles of RGB light-emitting type, and (c) RGB three-color light-emitting diodes; among these, the configuration (a) has become mainstream and is exemplified by a combination of a blue light-emitting diode and a YAG:Ce fluorescence substance, in which cerium (Ce) of an activator is introduced into yttrium aluminate (Y3Al5O12:YAG) of a base material of fluorescence substance to thereby exhibit blue color rendering (e.g., see Patent Document 1). Furthermore, a glass matrix, into which a transition metal ion has been introduced, causes light absorption in a visible light region or fluorescent emission in a near-infrared region and thus can be used as a fluorescent substance through the use of a high intensity emission. There has been provided a glass material containing a monovalent copper ion (Cu+ ion) and exhibiting blue fluorescence as such a fluorescent substance (e.g., see Patent Document 2).    Patent Document 1: Japanese Unexamined Patent Application, Publication No. H10-36835    Patent Document 2: Japanese Unexamined Patent Application, Publication No. H10-236843